Field of the Invention
This invention relates to a fuel supply control system for an engine.
Description of the Prior Art
It has been known to increase the fuel supply to an engine during operation under heavy load in order to increase engine output power, as disclosed in Japanese Unexamined Utility Model Publication No. 54(1979)-124822 and U.S. Pat. No. 4,488,529, for instance. However, in such engines, the fuel increasing characteristics according to which the fuel supply is increased during heavy load operation have conventionally been determined irrespective of whether the vehicle is provided with an automatic transmission or a manual transmission, and accordingly, fuel economy is apt to be deteriorated as power transmission efficiency is lowered in the case of a vehicle having an automatic transmission.
Further, the fuel increasing characteristics according to which the fuel supply to the engine is increased when the fuel requirement is increased such as during heavy load operation of the engine are set so that the air-fuel ratio can be a value that ensures sufficient engine output power even if the vehicle is required to accelerate under such conditions.
That is, when the engine output power requirement is increased when the engine is operated under a heavy load, a fuel increase correction is effected to increase the fuel supply to make the air-fuel ratio richer than that in the normal operation of the engine. When the increasing rate of the fuel supply in the operating range is reduced in the case where the vehicle has a manual transmission, increase in engine output power becomes insufficient and increase in engine speed lags, thereby deteriorating acceleration performance and giving rise to fluctuation in engine output power, since during acceleration in the case of the manual transmission the load acts directly on the engine by way of the transmission. Further, when combustion in the combustion chambers is unstable such as during warm-up of the engine, small fluctuations in load can change engine output power by a large amount, and accordingly, also in such a case, a fuel increase correction is effected to enrich the air-fuel ratio, thereby ensuring sufficient engine output power. Also in this case, if the fuel supply increasing rate is relatively small, fluctuation in the engine output power due to fluctuation in the combustion in combustion chambers is transmitted directly to the driving wheels, deteriorating the operating performance in the case of a manual transmission.
On the other hand, in the case of an automatic transmission having a torque convertor, momentary load fluctuations cannot be transmitted, and engine output power is not transmitted to the driving wheels until the engine output power and engine speed are increased in response to an accelerating operation. Further, in the case of an automatic transmission, load fluctuation has a lesser effect on the engine during warm-up and stable operating performance can be obtained.